The field of the invention is systems and methods for medical imaging. More particularly, the invention relates to systems and methods for improving tractography and tractographic processes, for example, by producing and using a subject-specific coordinate system that conforms to a tissue of interest or considering the interrelation of tracts during tractography or processes related to tractography.
Understanding brain connectivity on a global scale is likely a prerequisite to understanding brain function. Whereas studies in animals with tract-tracers have identified individual pathways and their topology as complex networks, studies of the geometric organization of connectivity in the context of brain evolution, development, plasticity, neural coding, and large-scale cerebral specialization have suggested much simpler organization. The need to synthesize these disparate viewpoints is long recognized and has prompted technical innovation and basic discovery. That is, the research and development to date has been able to capture small and explain small portions of the overall brain architecture, but there has been a clear desire to determine a single view to brain. However, while progress has been achieved outside the forebrain, no single picture yet describes both the geometric and topologic character of cerebral connectivity. Particularly, it has been significantly difficult to accurately map cerebral pathways in an anatomical context, or anatomical relations between pathways in a single brain.
The large-scale structure of the primate cerebral connectome—the totality of fiber pathways of the cerebral white matter—has been elusive. In the late 19th to early 20th century investigations of connectional neuroanatomy using traditional dissection and microscopy uncovered basic principles of large-scale brain organization and development. By the mid 20th century, these methods were supplanted by more precise and reproducible methods of fiber tracing. The success of the fiber tracing approach, and its emphasis on point-to-point connectivity, however, tended to remove from view questions about the organization of the brain at larger scales. The three-dimensional relations between fiber pathways are difficult to discover with fiber tracing techniques, and the presumption is often made that these relations are of secondary importance.
Recently, magnetic resonance imaging (“MRI”) methods, such as diffusion MRI, have been developed to map major fiber pathways in a single brain. Diffusion MRI now affords a means by which to map the connectional anatomy of a single brain in its entirety, and to do so rapidly, three-dimensionally, nondestructively, and noninvasively. In the development of this technology, a key advance was the recognition of the problem of ubiquitous fiber crossings in the brain. The difficulty fiber crossings posed for early diffusion tensor imaging (“DTI”) mapping of fiber pathways helped lead to the development of methods for accurately resolving fiber crossings, such as diffusion spectrum imaging (“DSI”), Q-Ball imaging, q-space imaging (“QSI”), and other related techniques. While these methods provide an ability to resolve complex fiber architecture at each location, the quantitation of complex fiber architecture and of diffusion beyond the tensor remains challenging, and an active area of research.